Field of the Invention
The present invention relates generally to a strap-type wrench for removing rotatable closures, and more particularly to an improved strap-type wrench having two rings to assist in removing the slack in the gripping strap, and a pressure plate with a frictional gripping surface positioned on the wrench to allow the frictional gripping surface to be forced radially inwardly against the object being gripped by the wrench, thereby enhancing the frictional grip of the frictional gripping surface on the object.
Strap-type wrenches of widely varying designs have proliferated over the years, with the wrenches being for the most part separated into two different design categories. These categories are, first, wrenches having flat metal bands as the gripping surface, and secondly, wrenches having flat fabric straps as the gripping surface. The first of these categories primarily includes wrenches used for oil filters, with typical examples being U.S. Pat. No. 3,686,984, to Kelso, U.S. Pat. No. 3,838,615, to McFarland et al., U.S. Pat. No. 3,728,916, to Brantley, U.S. Pat. No. 4,158,974, to Yamashita, and U.S. Patent No. 4,598,615, to Tate. These devices differ mainly in the camming mechanism used to tighten the metal band. Also in this category is U.S. Pat. No. 3,964,115, to Platek, which is a device for removing jar tops.
The wrenches in this first category all suffer from several disadvantages. First, since a relatively rigid metal band is used, these devices are not practically adjustable, since the metal bands used in the devices are not of adjustable length. The implication of this fact is that the wrenches in this category are useful only on articles within a relatively small size variation. The implication of this point is enhanced through an understanding that the size of oil filters varies substantially, therefore requiring several different wrenches to enable the removal or installation of all of the various filters.
Another disadvantage of this first category of wrench is that the metal bands tend to slip somewhat when used on smooth round surfaces. This is particularly a problem in the removal of oil filters, which are likely to have oil on the outer surface thereof. Still another disadvantage of the first category of wrench is that they are necessarily of larger size than wrenches in the second category. This is readily apparent since the metal bands do not collapse for storage. It will be realized by those skilled in the art that compact size is a distinct advantage, since most owners of such wrenches will have a number of tools and a limited amount of storage space for the tools.
The second category, wrenches having flat fabric straps as the gripping surface, is illustrated by U.S. Pat. No. 689,325, to Sands, U.S. Pat. No. 840,496, to Justen, U.S. Pat. No. 3,678,788, to Matti, U.S. Pat. No. 4,345,494, to Aamodt, and U.S. Pat. No. 4,532,833, to Downs. These wrenches offer the advantages of being useable on widely varying sizes of articles and of being compact of size, both of which advantages are due to the use of a fabric strap rather than a metal band. However, the known designs of such devices are not without disadvantage.
For example, in some of these wrenches there is no positive retention of the free end of the strap, thereby allowing the strap to expand in size due to slippage, as illustrated by the Justen device. Several of the above devices get around this by having positive adjustment stops for the free end of the strap, as taught by the Sands reference. This makes the wrench more difficult to use, since the appropriate adjustment must generally be found by trial and error. It also undesirably results in a wrench having several discrete sizes rather than being infinitely adjustable.
However, the biggest single disadvantage of the second category of wrench is that it also has a tendency to slip on smooth round surfaces, like the wrenches in the first category. It is readily apparent that a woven nylon strap, which is the most commonly used flexible fabric strap, does not have a high coefficient of friction which will enable the wrench to strongly grip the surface of smooth round articles, such as oil filters. In the final analysis, grip strength is the most important single element of a strap-type wrench, and the wrenches in the second category have a distinct disadvantage, with even the far from ideal wrenches of the first category out performing them on this count.
It is accordingly the primary objective of the present invention to provide a strap-type wrench which will be highly resistant to slippage on the article being gripped, even if that article is a smooth round surface. Such an improved wrench must of course remain useable on all types and configurations of surfaces, not being limited to use on cylindrical surfaces only. It is also an objective of the present invention that it utilize a fabric strap, thereby being of inherently smaller size than wrenches in the first category.
It is an additional objective of the present invention that the wrench be infinitely and easily adjustable. It is desirable that this be accomplished without requiring discrete positive adjustment stops for the free end of the strap, the elimination of which makes the wrench easier to use. It is desirable that the wrench be infinitely adjustable rather than having several discrete sizes, thereby allowing the appropriate adjustment to be made quickly and easily rather than being found by trial and error.
It is an additional objective of the present invention to allow for quick and easy adjustment of the strap around the object being gripped. Finally, it is also an objective of the present invention to provide a positive retention of the free end of the strap to prevent the strap from expanding in size due to slippage. This positive retention should be a function of the design of the wrench rather than being an additional control, or requiring a positive step to be performed to secure the strap against expansion. The wrench of the present invention should also be of inexpensive construction, thereby giving it an economic advantage as well. Finally, the improved wrench of the present invention should provide all of the aforesaid advantages and objectives without incurring any relative disadvantage.